The present invention relates to the problems of supply of a plurality of hydraulic work units from a common power station and more particularly to the problems encountered for example in transfer-machines, comprising a plurality of work units with a fixed station, carrying out different work cycles controlled in accordance with appropriate programming from a hydraulic power supplied by a common production unit.
In the machines of the above type, it is known that it is considered as advantageous, regarding cost and operation price, to provide only one hydraulic station for supplying the various work units or stations of the same machine effecting different cycles which develop according to an appropriate programming. A concept of this type raises however a problem since, for example, when one of the work units is in fast return phase between two successive machining phases, a momentary drop of pressure occurs in the supply circuit which is common to all units. A pressure drop of this type is detrimental to the correct operation of the other units in machining phase since the hydraulic power transformers which control the tools are subject to rushes which are highly prejudicial to the quality of the work executed, in particular in the finishing stage. In some cases, these rushes may even cause breaking of fragile tools.
For solving this problem it has already been proposed to use, for each of the supply circuits suitable for a unit or a work station, a control device of the slide valve type, the respective positions of which are controlled by the pressure variations of the circuit, upstream and downstream. An apparatus of this type, even if it permits to solve the problem, has two obvious drawbacks. The first drawback is its complex design which requires a complicated and accurate machining resulting in a high cost and maintenance price. The second drawback results from the fact that it is necessary to connect the different upstream and downstream pressure sources, so that mounting such an apparatus in a conventional supply circuit substantially complicates the circuit, in particular by requiring subsidiary apparatus for its operation.
The aim of the present invention is to obviate the above drawback by solving the problem, and to this end, the invention suggests a new control unit which can be very easily adapted to the supply circuit of each work unit or station while requiring only one main direct connection and the setting up of a secondary direct feedback circuit between the said apparatus and the fluid reservoir. In addition, the subject matter of the invention is conceived in a particularly simple manner in order to be of a relatively low price and to have low maintenance costs, considering the good possibilities of access to the various movable constitutive parts which can be subjected to wear or deterioration.
According to the invention, the unit controlling the supply of a work unit fed in parallel from a hydraulic station common to other units is characterized in that it comprises, between an inlet well and an outlet well for the fluid under pressure, closure means urged into the closed position by a resilient member located in a chamber communicating with a conduit issuing from the outlet well so as to act against the pressurized fluid delivered in the inlet well and separated from a feed back conduit to a reservoir by a relief valve urged in the closed position by means of a resilient member and by the fluid pressure prevailing in the inlet well.
Other characteristics will become apparent from the following description made with reference to the accompanying drawing, which shows as a non-limitative example, an embodiment of the subject matter of the invention.